1. Field of the Invention
The present invention generally concerns shipboard design to combat Aquatic Nuisance Species (ANS) invasion resulting from ballast water discharge.
The present invention particularly concerns ballast water treatment, deoxygenation and carbonation of ballast water, reduction of pH in ballast water, infusion of inert gas into ballast water, control of aquatic nuisance species, bubbling of inert gas through and into ballast water, and elevated CO2 levels in ballast water.
2. Background of the Invention
2.1 Aquatic Nuisance Species Present in Ship's Ballast Water
It is estimated that 21 billion gallons of ballast taken on in foreign ports are discharged by commercial vessels annually in the waters of the United States (Carlton et al. 1993). Ballast water transport is a major vector for introduction of potentially invasive aquatic species.
Standards for treatment of ballast water are still in a state of flux. Efforts to define standards are ongoing in the US Congress, International Maritime Organization (IMO), and other individual maritime nations. The US Congress (NAISA 2002) proposes an Act that will, among other considerations, set the interim standards for ballast water treatment (BWT). It stales, “The interim standard for BWT shall be a biological effectiveness of 95% reduction in aquatic vertebrates, invertebrates, phytoplaokton and macroalgae.” There are discussions about setting micron standards, i.e. x microns cut-off for living organisms. Currently, a fifty (50) micron standard is being discussed in various circles, including IMO and US Coast Guard. The default standard appears to be the Ballast Water Exchange (BWE), or something close to it. Cangelosi (2002) states “ . . . the Coast Guard has set forth a “do-it-yourself” approach, directing interested ship owners to conduct complex shipboard experiments (post-installation) to undertake direct and real-time comparisons between BWE and treatment. If the comparison is favorable and defensible, the Coast Guard will approve the treatment. See Cangelosi, Allegra (Nov. 14, 2002). Testimony Before the Joint Committee on Resources and Science of the U.S. House of Representatives.
2.1 Control of Aquatic Nuisance Species Present in Ship's Ballast Water
Glosten (2002) provides a review of the numerous treatment systems for the control of aquatic nuisance species in ship's ballast water. These systems include heat, cyclonic separation, filtration, chemical biocides, ultraviolet light radiation, ultrasound, and magnetic/electric field. See Glosten-Herbert-Hyde Marine (April, 2002). “Full-Scale Design Studies of Ballast Water Treatment Systems”, Prepared for Great Lakes Ballast Technology Demonstration Project.
Known methods not mentioned in this reference are hypoxia, carbonation, and their combination. In studies of 18 months duration on a coal/ore vessel (Tamburri et al. 2002), the ballast water dissolved O2 level was reduced and held to concentrations at or below 0.8 mg/l by bubbling essentially pure nitrogen. See Tamburri, M. N., Wasson K., and Matsuda, M. (2002). Ballast water deoxygenation can prevent aquatic introductions while reducing ship corrosion. Biological Conservation. 103, 331-341. The experiments resulted in a treatment “that can dramatically reduce the survivorship of most organisms found in the ballast water . . . ”
In extensive experiments with gas of varying percent CO2, N2 and O2 (McMahon, et al. 1995), the “ . . . results indicate that CO2 injection may be an easily applied, cost-effective, environmentally acceptable molluscicide for mitigation and control a raw water system macrofouling by Asian clams and zebra mussels”. See McMahon, R. F., Matthews, M. A., Shaffer, L. R. and Johnson, P. D. (1995). Effects of elevated carbon dioxide concentrations on survivorship in zebra mussels (Dreissena polymorpha) and Asian clams (Corbicula fluminea). In The fifth international zebra mussel and other aquatic nuisance organisms conference, pp. 319-336. Toronto, Canada.
2.3 Corrosion Considerations of Various Ballast Water Treatment Systems
Shipboard corrosion mitigation is always a priority consideration. It requires the continual attention of the crew and, if not carefully controlled, can actually compromise the strength of the ship. Any installed ballast water treatment system must not under any circumstances increase the potential for corrosion, and if possible, should decrease the potential. The present invention will be seen to have considered the corrosion issue.
As reported in literature Tamburri et al. (2002), corrosion might even be mitigated by deoxygenation. See Tamburri, M. N., Wasson K., and Matsuda, M. (2002), op cit.
Perry, et al. (1984) state that unless pH level drops below 4 concerns about corrosion are unfounded. See Perry, R. H., Green, D. W., Maloney, G. O. Perry's Chemical Engineer's Handbook, 5th Ed., McGraw Hill, 1984.
2.4 The Theory of Ballast Water Treatment by Anoxia and/or Hypoxia
Except for ballast water exchange, essentially all treatment concepts involve the chemical change of the water to cause an environment lethal for ANS. The chemical changes described in Tamburri et al. (2002) and McMahon (1995) offer promising results, i.e., reduce the dissolved O2 in the one case, and carbonate and reduce the pH in the other case. See Tamburri, M. N., Wasson K., and Matsuda, M. (2002), op cit. See also McMahon, R. F., Matthews, M. A., Shaffer, L. R. and Johnson, P. D. (1995), op cit.
In both cases the process involves the exchange of gases, the extraction of the dissolved O2 and the introduction of CO2. Surface contact area and partial pressure differentials permit the gas exchanges to occur. The deoxygenation of the ballast water is based on Henry's Law of gas solubility: The relative proportion of any dissolved gas including oxygen in the ballast water is a function of the concentration, equivalent to partial pressure of the gas (e.g. oxygen), within the mixed gases over the ballast water. The depletion of oxygen in the ballast water is primarily a function of the shared surfaces and concentrations at the interfaces of the inert gases and water.
The pH of the ballast water is lowered by the chemical reaction:CO2+H2O→H2CO3⇄H++HCO3−
This equation is interpreted that carbon dioxide (CO2) reacts with water (H2O) to form carbonic acid (H2CO3), which then partially dissociates to form hydrogen (H+) and bicarbonate ions (HCO3−).
All systems described thus far in the literature, including ballast transfer, have left untreated the sediment buildup in the bottom of the tanks. If the orifices in the lattice work of piping were to point down, then the sediment could potentially be stirred up, facilitating the killing of the embedded ANS.
2.2 Ballast Water Treatment in the Related Predecessor Patent Application
The user of gaseous underpressure in the treatment of ship's ballast water so as to combat Aquatic Nuisance Species (ANS) invasion resulting from ballast water discharge, described in this application, is an extension of American Underpressure System (AUPS) of MH Systems, San Diego, Calif. The AUPS utilizes a slight negative pressure in the tank's ullage space, in an inert environment, to prevent or minimize oil spillage from tankers (Husain et al. 2001). See Husain, M., Apple, R., Thompson, G. and Sharpe, R. (2001); Full Scale Test, American Underpressure System (AUPS) on USNS Shoshone, presented to Northern California Section, SNAME, September 2001.
The American Underpressure System (AUPS) is the subject of U.S. Pat. No. 5,156,109 for a System to reduce spillage of oil due to rupture of ship's tank, and U.S. Pat. No. 5,092,259 for Inert gas control in a system to reduce spillage of oil due to rupture of ship's tank. It is also the subject of related U.S. Pat. No. 5,343,822 for Emergency transfer of oil from a ruptured ship's tank to a receiving vessel or container, particularly during the maintenance of an under-pressure in the tank; U.S. Pat. No. 5,323,724 for a Closed vapor control system for the ullage spaces of an oil tanker, including during a continuous maintenance of an ullage space underpressure; and U.S. Pat. No. 5,285,745 for System to reduce spillage of oil due to rupture of the tanks of unmanned barges. All patents are to the selfsame inventor Mo Husain who is one of the co-inventors of the present invention.
The AUPS is retrofittable on existing tankers, and has the similar spill avoidance capability as that of a double hull tanker during accidental rupture of the hull. The AUPS spill avoidance system creates a slight vacuum (two to four pounds per square inch) in each cargo tank. This vacuum, assisted by the outside hydrostatic pressure of the surrounding water, prevents or minimizes cargo loss in the event of hull rupture. In case of a bottom rupture caused by grounding, nearly all of the cargo can be protected. In the case of side hull damage, cargo below the level of the damage will be lost, while the cargo above the side hull rupture will be protected.
This system can be used in conjunction with existing inert gas systems that are mandatory on most tankers to prevent explosions. The AUPS consists essentially of exhaust blowers with their isolation and control valves tapping into the inert gas system. A negative pressure of inert gas is created in the ullage space—the volume of gas above the oil. This negative pressure or underpressure is continuously adjusted and prevents oil from spilling if the tanker is ruptured. Stated simply, the oil is held in the tank by the slight underpressure.
This partial vacuum, or underpressure, assisted by the outside hydrostatic pressure of the surrounding water, prevents or minimizes cargo loss in the event of hull rupture. In case of a bottom rupture caused by grounding, nearly all of the cargo can be protected. In the case of side hull damage, cargo below the level of the damage will be lost, while the cargo above the side hull rupture will be protected.
This negative pressure or underpressure is continuously adjusted and prevents oil from spilling if the tanker is ruptured. Again stated simply, the oil is held in the tank by the slight underpressure.
As of 2003, the environmental threat posed by oil tanker accidents has mandated the use of double-hull construction. However, the phase-out of conventional “single-skin” tankers may last to 2015. One goal of the AUPS system, including as is modified and enhanced by the present invention, has been and remains, circa 2003, to provide the protection until all existing single-skin tankers visiting U.S. ports are retired.
The present patent application is also related as a Continuation-in-Part to U.S. patent application Ser. No. 10/120,339 filed on May 9, 2002, for CLOSED LOOP CONTROL OF BOTH PRESSURE AND CONTENT OF BALLAST WATER TANK GASES TO AT DIFFERENT TIMES KILL BOTH AEROBIC AND ANAEROBIC ORGANISMS WITHIN BALLAST WATER to inventor Henry Hunter assigning to the same MH Systems, San Diego, Calif., that is the assignee of the present invention. That application is itself a Continuation-In-Part (C-I-P) of U.S. patent application Ser. No. 09/865,414 filed May 25, 2001, for CLOSED LOOP CONTROL OF VOLATILE ORGANIC COMPOUND EMISSIONS FROM THE TANKS OF OIL TANKERS, INCLUDING AS MAY BE SIMULTANEOUSLY SAFEGUARDED FROM SPILLAGE OF OIL BY AN UNDERPRESSURE SYSTEM, now issued as U.S. Pat. No. A,AAA,AAA.
As a simplified basis of comparison, the first related predecessor application may be considered to teach the control of oxygen in ship's ballast water maintained under a pressure less than atmosphere for the inducement, at different times, of both such (i) oxygen-starved and (ii) oxygen-rich conditions as are respectively fatal (i) to aerobic marine organisms (by action of hypoxia), and (ii) to anaerobic marine organisms (by action of exposure to high levels of dissolved oxygen).
Meanwhile, the present application will be seen to teach the inducement of each of (i) carbon dioxide-rich, (ii) acid-enhanced and/or (iii) oxygen-starved conditions in ship's ballast water—preferably as is continuously maintained under a pressure less than atmosphere pressure—so as to induce, at one and the same time, (i) hypercapnic, (ii) acidic and/or (iii) hypoxic conditions that are fatal to both aerobic, and anaerobic, marine organisms.